davis



Jan. 24, 1956 E. A. DAVIS 2,732,099

HOPPER CONTROL APPARATUS AND METHOD Filed D80. 6. 1950 2 Sheets-Sheet 1INVENTOR EDWARD A. DA W6.

/{ I 9 ATTORNEY 1956 E. A. DAVIS 2,732,099

HOPPER CONTROL APPARATUS AND METHOD Filed Dec. 6, 1950 2 Sheets-Sheet 227 H/Qfl r951 H27 l; I ZC' IEIIE IN VENTOR fDWA/Pi 9. DA W6.

United States Patent 2,732,099 HOPPER CONTROL APPARATUS AND METHODEdward A. Davis, Ruxton, Md., assignor to Gerotor May Corporation,acorporation of Maryland Application December 6, 1950, Serial No.199,489 9 Claims. (Cl; 222-1) My invention relates generally to storagebins and hoppers and the like, and particularly concerns both a methodand apparatus for insuring the unobstructed discharge from such bins ofmaterials contained therein.

An object of my invention is to provide a method for insuring the freeand unobstructed flow of materials through or from bins and hoppersadapted for the storage, loading and classification of an infinitevariety of generally granular materials, which method is at once simple,rapid, certain and predictable in results, involving a minimuminvestment in plant space, equipment and materials, demanding minimumlabor requirements of but moderate skill, and adjustable sensitively andaccurately to widely variant loading conditions maintaining within thebin or hopper.

Another object is to provide apparatus for facilitating unobstructedpassage of the granular contents through bins, hoppers and the like inrapid and sensitive response to the momentary load conditions prevailingtherein and which is certain, reliable and predictable in operation,-and which employs a minimum number of component parts which inthemselves are small, simple, rugged and readily available.

All these and many other highly practical objects and advantagesattendant upon the practice of my invention, which in part will beobvious and in part more fully pointed out hereinafter during the courseof the following description. 7

Accordingly, my invention resides in the arrangement parts, features ofconstruction, combination of elements, as well as in the severaloperational steps and the relation of each of the same with one or moreof the others as described herein, the application of all of which ismore fully set forth in the claims at the end of this specification.

In the several views of the drawings, wherein I have disclosed,illustratively, that embodiment of my invention which I prefer atpresent,

Figure 1 is a schematic elevation, with partsshown in section, wherein Idisclose the general assembly of apparatus according to the practice ofmy invention;

Figure 2 is a schematic view, on enlarged scale, wherein I disclose thecontrol mechanism employed in the apparatus of Figure 1; while Figures 3and 4 are sectional views showing the two control positions of a typicalthree-way valve employed in the apparatus of Figures 1 and 2.

Throughout the several views of the drawings like reference charactersdenote like constructional parts.

As conducive to a more ready understanding of certain features of myinvention, it may be noted at this point that in industrial ormanufacturing operations it frequently becomes necessary to storegranular or powdered material, thereafter channelling it to one or morepoints of use, and this either in continuous or intermittent manner.Morevore, it frequently is required to classify or grade such materialsas they pass from'the storage conice factory for this purpose. Usuallysuch hoppers have walls sloping with respect to the horizontal. Andmechanical take-off means are employed at the bottom of the hopper suchas a continuous belt, a worm or a rotatable disc, any of which serveseffectively to remove the processed substance from the discharge end ofthe bin.

It is well recognized, however, that difficulty frequently isencountered when the materials undergoing processing are finely dividedsubstances or those which are slightly damp. It is found that thesematerials occasionally are inclined to compaction, forming an arch at orabove the throat of the hopper as a result of the vertical pressures onthe material contained in the hopper, or forming a hollow cone againstthe walls of the hopper as a result of the horizontal pressuresencountered. These effects are especially pronounced in sticky materialsuch as foundry core mixes. Upon obstruction at the throat or along thewalls of the hopper, the materials jam and build up in back and on topof the obstructing material. With initial clogging, of course, theeffect builds up quickly, further intensifying the obstruction to theextent that operation of the hopper becomes uncertain and unpredictable.To ensure that the hopper contents flow readily and certainly ordinarilyrequires the constant attendance of an operator.

For one reason or another, therefore, the art has long sougth to providefor shaking, vibrating or pulsating the tainers. A hopper or storage binproves entirely satis-' collapsing the same.

material as it passes through the hopper, not so much as to break up thejammed material after jamming has taken place as to prevent the materialfrom jamming the hopper before such jamming occurs.

lllustratively, mechanical vibrators have been employed. These, however,are not readily employed in the conventional hopper fashioned of wood orof concrete. Moreover, these vibrators do not always shake down thematerial in the desired certain and satisfactory manner.

Elfort also has been directed towards providing elastic membranes ordiaphragms sealed at their margins to the interior surfaces of a hopperinto which the granular materials are charged. The seal between membraneand hopper wall is made air-tight and the membranes are pulsated byadmittance of air under pressure to the space between membrane and wall,the air being subsequently exhausted. This has the effect, in cyclicoperation, of initially distending or dilating the membrane, and thenExhaust of the space between membrane or hopper wall is accomplished bythe elasticity of the membrane itself, particularly as aided by the loadof the bin. Typical of this mode of operation is that disclosed in theUnited States Letters Patent to Tainton, No. 1,570,795, wherein athree-way air-control valve is motor-driven to control the pulsation ofone or more diaphragms provided in the hopper, these being mounted aspanels on the sloping surfaces of the bin. They are inflated anddeflated by admitting and exhausting air from the space defined by thediaphragm and the portion of the wall of the bin upon which thediaphragm is mounted.

In general the pulsating-wall type of operation proved substantiallybetter than the techniques theretofore available in the art. I find,however, that there is one important difliculty inherent in suchconstruction: there is a definite lack of flexibility in adapting theapparatus to the various load conditions maintaining within the bin, aspresented by passage of various types and consistencies of granularmaterials. Moreover, the compressed air line pressures-available in theaverage industrial plant tend to rupture the rubber diaphragms even whenthe latter are reinforced. To preclude rupture various air pressureregulators have been employed. But when these regulators are of a sizesuflicient to pass requisite unit was es.

and cam, and these in addition to the valve and pressure regulators,proved extremely costly.

To avoid the necessity of a high capacity air-pressure regulating valveit was proposed to supply a specialvalve. connected to and controlled bythe under-surface of the pulsating membranes of the panels. Thiswaswith. the thought that movement of the membrane itself would de terminethe moment at which air was either admitted into or exhausted from thespace defined by membrane and panel and the extent to which this was totake place, all

this by way of a valve mechanism physically remote from the membrane anddisposed exteriorally of the bin. Here again, however, a fundamentaldifliculty was encountered in that specially constructed equipment wasrequired. Moreover, sticking of the valves was noted, due probably tothe deposition of moisture and foreign particles in the closely fittingparts of the valve from the air and dust about the bin or hopper withwhich the panel was associated. A final difficulty remained, notably,that unless air pressure regulation-just what it was sought to avoidwasagain resorted to, then the proposed controlv was too insensitive forpractical operation. For it was found that where an upper portion of thepanel became exposed in the course of emptying the bin or hopper, thenthis exposed portion of the membrane inflates to the point of rupturebefore correction is provided by suificient movement of that portion ofthe membrane bearing the connection to the control valve.

Thus, for one reason or another, the bin control, expedients heretoforeavailable in the art, unfortunately, have proved to be satisfactory.Either they have been impractical or else they have been too costly,both of initial installation and subsequent maintenance and operation.Requirements of simplicity and low first cost were not satisfied, norwere the three-fold requirement of certainty, rapidity, and sensitivityof operation. Long, useful life could not be achieved.

A further object of my invention, therefore, is to avoid in substantialrespect the many disadvantages and defects resident in the prior art,and at the same time to provide both a method and an apparatus whichwill. properly, sensitively and accurately pulsatethe membranes of thebin panels in close response to the'load con.- ditions therein withoutdanger of rupture ofrthe membranes and with long useful life, withoutclogging the bin or hopper, requiring only componentparts which inthemselves are simple, inexpensive, reliable and certain, which arereadily available on the market and which require minimum supervisionand attendance.

Turning now to a consideration of my invention, and having reference tothe several views of the drawings, I provide a hopper or bin indicatedgenerally at 10 (Figure l) for the storage and delivery, as the case maybe, of the generally granular or flaky material. While it may beconstructed of any suitable material I conveniently employ sheet metalofsubstantial gauge, displaying good wear qualities. The hopper may haveany desired and suitable shape with a charging opening at thetop; and adischarge opening at the bottom to assure gravity discharge. In atypical embodiment disclosed, I provide a conical bin symmetrical abouta vertical axis and displaying a circular cross-section with suitableopenings at top and bottom.

As stated, bins and hoppers of the generaltype noted 7 may be used, fora varietyv of: purposes, illustratively, storage, delivery in meteredsupply either; continuously 4 or intermittently with volume eithervarying or continuous 'in amount as desired, for classification ofmaterial from one sorting container to another, as well as for a varietyof other and generally similar usages. Take-off from the bottom outletof the bin may be accomplished in a variety of conventional manner, asheretofore indicated. Illustratively, a rotating screen, a continuouslyrotatable worm, or the like is provided at the bottom of the hopper.Since these elements are conventional, however, and comprise no part ofthe present invention specific disclosure thereof is dispensed with inthe interest of simplicity and clarity.

Now, if the material undergoing handling be dry and displays rounded,smooth surfaces, it is unlikely that any real difficulty will beexperienced during its passage through the hopper. But, when thematerial being handled is flaky and displays a rough surface, wherebyadjacent particles can interengage with each other, or where thematerial is damp, and particularly when the granular substance is lightin weight, jamming frequently is inclined to occur, along the narrowedthroat portion of the hopper in the region discharge.

Accordingly on the interior surfaces 11 of the inclined walls of thehopper in the region where jamming is likely to occur of the granularcontents of the bin, I provide one or more membranes 12. These membranesare formed of elastic material, of which rubber, either natural orsynthetic, is typical, conventional and suitable. Each membrane 12 ismade fast to a metal plate 14, illustratively steel, and these platesare secured in desired convenient manner to the walls of the hopper 10as for example by bolts 13. The combination of membrane and plateconveniently is referred to as a panel.

The membranes 12, shown in collapsed position by solid lines in Figurel, are intended for distension in pulsating manner by air admitted tothe panel, that is, between membrane and back plate. The pulsation ofthe membranes imparts a pulsating movement to the contents of the hopperthereby eliminating static compression stress zones or arches, eitherhorizontal or vertical, supporting overlaying material. This, of course,has the effect of preventing the jamming of the contents of the bin.Both the frequency of pulsation and the amplitude of the same may beadjusted to respond most satisfactorily to the load conditionsmaintaining within the bin. Thus, when the tendency toward jamming isslight, the frequency of cyclic inflation and deflation of the panels,may be decreased, and along with it the amplitude ofinfiation. And whereit is substantial the frequency and amplitude may be increased. Atypical inflated position of the panels with distension of the membranesis indicated in dotted lines in Figure 1 at 12A.

I. find that it is not enough simply to inflate and deflate the panels12, 12with fixed frequency; it is required, for really satisfactoryoperation, that the control be pressureresponsive, and that means beprovided for adjusting the pressure limits to which the controlresponds. The apparatus now to be disclosed is directed to thatobjective.

An air line, consisting of metal piping indicated generally at 15, leadsfrom a control unit, indicated generally at 16 (Figure 1), to the panels12, 12. At 15 the pipe line 15, illustratively of half inch diameter,separates into branch circuits 15A, 15A, provided one for each panelwithin the hopper; In the illustrative embodiment, two such panels areprovided, so that there are two branchlines 15A, 15A. In suitable mannerthese branch lines let through the walls 11 of the hopper 10 and throughthe steel plates 14, opening directly into the spaces defined by theplates and corresponding membranes 12, 12. The pipe line 15 serves toadmit air to the panels and, to exhaust the latter to the atmosphere,likewise through the control 16. The details of this control 16 are bestshownin Eigure 2.

Having reference now: more. particularly to, Eigure 2 it, will be; seen,that although part. of the: control 16 is disposed exteriorally of thecasing 17 thereof, this control is provided and installed as a singleunit. Control 16 is connected to a suitable source of air supply by wayof conduit 18. This air supply is usually maintained in industrialpractice at a pressure of some 80 to 150 pounds per square inch.

In order to control the frequency of pulsation, I provide, within thecontrol 16, a valve indicated generally at 19 and directly in line withthe air line 18 by union 20 or generally similar connection. Valve 19 isprovided with conventional stem 19A and handle or other control means19B. When control 16 is in use the valve 19 is cracked open only to anextent which will cause inflation of the panels just suflicient to keepthe material moving satisfactorily through the hopper 10. Furtheropening of valve 19 has the efiect of permitting air to more quicklyinflate the panels, thereby increasing the rate of pulsation of thepanel membranes 12, 12.

It. will be recalled that in order to properly .efl'ect operation of thepulsating membranes, they must first be provided, according to adeterminable cycle, with air to inflate the panels with which they areassociated and then be subjected to collapse by suitable exhaustion ofair within the panels. During a portion of any cycle of operations theair from conduit 18 and valve 19 is provided to the panels. Membranes12, 12 are, thus distended. The amount of distension, or the amplitudeof the pulsators, is controlled by a suitable valve dependent upon thepressures reached within the panel as appears more fully hereinafter.When the predetermined distension, or rather, the predetermineddistension pessure is reached in the cycle the flow of air to the panelsis terminated and these latter are connected to the exterior throughconduits 15A, 15' and 15 and control 16. At this point in the operatingcycle the load within the hopper 10, as well as the elasticity of themembranes, collapses the same and exhausts the panels to the exterior.

To bring about the intermittent action I provide within control 16 athree-way solenoid valve indicated generally at 21, and having its inletport connected directly in line with the valve 19. Ths solenoid valve21, which in itself is conventional has a valve stem 21A (Figures 3 and4) which passes through the solenoid winding not shown and is connectedto a ported valve piston 21B. The piston passes generally through acylindrical opening 21C defined by valve walls 21D. Throttled-air line22 (Figures 2, 3 and 4) lets through the left-hand cylinder wall 23(Figure 3) into the cylinder 21C.

In the de-energized position of the solenoid as shown in Figure 4, andupon cracking the valve 19 to start the apparatus into operation, theair through pipe 22 passes through the ports 23A and 23B of the solenoidcylnder 218 to the line 24, which latter, it will be called, conveys airto the panels with membranes 12, 12. In the energized position, asillustrated in Figure 3, the solenoid rod 21A brings piston 21B intoposition which breaks the channel connection between conduit 22 andchannel 23A. The piston then establishes a connection between panel line24, channel 23B, channel 230 and exhaust pipe line 25. This latterpasses exteriorally of housing 17 and opens directly to the atmosphere.

For the control of solenoid valve 21 I provide a pressure switchindicated generally at 26 connected to air-line 24. This pressure switchis itself of conventional type such as is now readily available on theopen market and its details of construction in large measure are omittedin the interest of clarity. The switch is provided with a low limitpressure adjustment indicated generally at 26A (Figure 2). Usually, andby way of illustration, this is set for actuation of the switch at apressure of approximately one pound per square inch in air-line 24-15.-A high pressure adjustment, indicated' generally at 26B, is provided toassure reverse actuation of the switch when a predetermined maximumpanels.

pressure is reached in the line. I find that in my apparatus an upperlimiting pressure of thirteen pounds per square inch usually issufiicient. The setting of the adjustment 26B determines the particularpressure in line 24-15 at which the admission of air to the line, andhence to the panels and membranes 12, 12 is cut-off during the course ofeach operational cycle. The pressure switch 26 is a control for makingand breaking electrical contacts, and determines the moment of makingand breaking the electrical operating connections for the solenoid valve21.

As air passes through the valve 21 when the valve 19 is cracked open, itpasses through three-way valve 21 in the rest position of the latter, asshown in Figure 4. Air then passes through lines 24 and 15 to .thepanels having flexible membranes 12. These latter are thereby distendedagainst the load within the bin or hopper 19. At the same time, part ofthe air passing through line 24 is branched to line 26C leading directlyto the pressure switch 26.

Air-pressure builds up within the switch 26 to the same extent as in thepanels until a critical value is reached, responding to the particularsetting of the high pressure limit adjustment 26B provided. When thispressure is reached the switch is actuated to operate solenoid valve 21,this by way of an electric circuit from the electrical supply line 29through leads 27, 27 and leads 2'7, 27 passing directly to solenoidvalve.

When valve 21 is operated in the manner indicated, the latter assumesthe Figure 3 position, discontinuing air supply from valve 19 and pipe22, and connecting the panel air line 15 by way of lines 24 to theexhaust conduit 25. As the air passes through line 24 towards theexhaust pipe 25 the pressure falls off in the switch 26 until there isreached the no-load limit pressure setting of adjustment 26A.

When switch 26 acquires its no-load position, it again is actuated, thistime however, to bring the solenoid valve 21 into the Figure 4 position,re-establishing the air circuit connections between valve 19 and thepanels. The cycle of operation then begins anew.

The control had with the pressure switch 26 is rapidand sensitive and isentirely unaflected by conditions maintaining within the hopper. Thepressure-actuated diaphragm or element within switch 26 is affectedsolely by the air-pressures within the line 24 and associated line 15.Thus, the supply of air to the panels and the flexible membranes 12, 12is entirely a function of pressure maintaining in the panels and thelines supplying them.

In my apparatus, I preferably employ a safety valve 32. suitablyconnected between the line 24 from the pressure limiting switch and theline 15 to the inflatable Thus air line 24, as regulated by switch 26,passes through the wall of container 17 to a four-way fitting 31, beingconnected thereto at 31A. The panel air line 15 is connected to fitting31 at 318. An airpressure gauge, not shown, may be connected to 31 at31C, here shown as plugged. The safety valve 32, of conventional design,is connected to fitting 31 at 31D. I provide this latter with amechanical trip member 32A. It should be operated occasionally, toinsure freedom of pop-off action. Usually this safety valve is adjustedto release at a pressure of 15 pounds per square inch.

It will be apparent from the foregoing that my new control need beoperated only when the hopper is actually in operation. Completeshut-down is achieved by disconnecting the source of electrical supplyto the incoming lines 29 and closing valve 19. When control 16 is inservice, the valve 19 and pressure switch 26 are adjusted to produce arate of pulsation and of amplitude best suited for the particular loadconditions. These'adjustments, as more particularly noted above, may bechanged readily and rapidly as load conditions vary; Unlike "the earlierexpedients' first introduced, wide variation in'"ad-' justment' of bothspeed and amplitude is effectively and readily achieved.

' Moreover, since thecontrol is provided at a point which is removedfrom the panels undergoing control, amore sensitive assembly iselfectively achieved. free of the dust and vibration of the hopper orbin. No danger of membrane rupture is encountered even through it may bemomentarily exposed by the load passing through the associated hopper.This attends upon effective control of the maximum panel pressure by theupper limit position of the pressure switch 26. Since the assemblyutilizes a true control, on which are placed no power demands, the partsthereof may be kept quite small. A variety of substantial economies arethereby achieved. The entire assembly is of low first cost and iscertain andpredictable in operation. Minimum maintenance orattendance isrequired, and the system displays long useful life.

Moreover, as a further advantage, the control itself readily may beconnected to and disconnected from the hopper or bin with which it isassociated. Accordingly, therefore, one control readily may serve anumber of bias or hoppers provided with expansible panels. And it'serves a variety of hoppers whether fashioned of steel, wood orconcrete.

It is apparent from the foregoing that once the broad aspects of myinvention are disclosed, many embodiments thereof will readily suggestthemselves to those skilled in the art. Additionally, many modificationsof the present embodiment will likewise be suggested. Accordingly, Idesire the foregoing disclosure to be considered simply as illustrative,and not by way of limitation.

I claim as my invention:

1. In combination, a hopper for the passage therethrough of granular andgenerally similar substances; an elastic membrane provided on theinterior wall of said hopper and adapted to be distended and collapsedin pulsating manner, through the admittance and expulsion of' air behindsaid membrane; a source of high pressure air; an air line connectingsaid source with said hopper wall and membrane for admitting air betweenthe same; and a control means in said air line and physically removedfrom said hopper, said control means including means for throttling thehigh pressure air, valve means for intermittently and alternatelyconnecting the membrane air line, first with the throttled air and thenwith an exhaust line to the atmosphere, and a pressure switch operableas an incident to the pressure of air in said line and membrane, tocontrol, upon reaching its low pressure and high pressure limitpositions, the operation of'said valve means.

2. In combination, a hopper for the passage therethrough of granular andgenerally similar substances; a panel with elastic membrane provided onthe interior wall of said hopper and adapted to'be inflated andcollapsed in pulsating manner; an air line connected with said panel foradmitting air therein; and a control means physically removed from saidhopper, said control means being provided in line with a source of highpressure air and said panel and including means for throttling the highpressure air, electrical solenoid valve means for intermittently andalternately connecting said panel air line, first with the throttled airline and then with an exhaust line to. the atmosphere, and an electricswitch operated by air pressure of said panel to control, upon reachingits low pressure and high pressure limit positions; the operation ofsaid solenoid valve, and means for adjusting the said limit positions ofsaid pressure switch.

3. Control apparatus, comprising in combination, inlet means connectiblewith a source of air under positive pressure; throttle. means in linewithsaid inlet means for controlling, the. flow therethrough; outletmeans. con: nectibleg. with a: load. to be. supplied by said. air;exhaust meansgconnectihle-with the atmosphere; a threefway-valve Itisphysically interconnectingsaid outlet. means with a selected one ofsaidinlet means and exhaust means; and a pressure responsive pressureswitch physically connected with said outlet means and.electricallyconnected with said three-way valve, and controlling saidvalve, in re sponse to air pressure Within said outlet means, forchangingthe position of said valve when the said pressure switch reachesits limit position of maximum pressure and minimum pressure.

4. Control apparatus, comprising in combination, inlet means connectiblewith a source of air under positive pressure; throttle means in linewith said inlet means for controlling the rate of flow of airtherethrough; outlet means connectible with a load to be supplied bysaid air; exhaust means connectible-with the atmosphere; a three: wayvalve physically interconnecting said inlet means, said outlet means andsaid exhaust means in such manner as to operably connect said outletmeans with a selected one of said inlet means and exhaust means whiledisconnecting the same with the other of the two lastmentioned means; apressure responsive switch physically connected with said outlet meansand electrically connected with said three-way valve, and controllingsaid valve, in response to air pressure within said outlet means, forchanging the position of said valve when the said pressure switchreaches its high pressure and low pressure limit positions and havingadjustments for changing the limiting operating pressures; and safetymeans in line withsaid outlet means for venting the same upon excess airpressures being reached therein.

5. As part of a pulsating control for facilitating operation of storagebins and hoppers wherein panels with elastic walls are provided withinthe bin or hopper adapted to be inflated and collapsed in pulsatingmanner through the admission and voidance of air led thereto through anair line, a control for regulating the passage of air through saidpanels provided in the air line to said panels but physically removedfrom the latter and in circuit with said air line, said controlcomprising: inlet means adapted to be connected with a positive pressureair supply; outlet means-for leading the air to the panels; exhaustmeans for conducting exhaust air to the atmosphere; a three-way valvefor connecting the outlet means with a selected one of said inlet meansand said exhaust means; and an air pressure switch controlled by thepressure in said panel line and connected to said valve so as to operatethe same upon obtainment of high pressure and low pressure limitpositions of the said switch.

6. As part of a pulsating control, inlet means adapted to be connectedwith a positive pressure air supply; a throttle valve connected withsaid inlet means; outlet means for the throttled air; exhaust means forconducting exhaust air to the atmosphere; a three-way solenoid valve forconnecting the outlet means with a selected one of said inlet means andsaid exhaust means, the connection of said outlet means to either one ofthe two last-mentioned means being terminated upon establishment of itsconnection with the other of the two last-mentioned -leans; and an airpressure switch connected to the outlet line and electrically connectedthrough a source of electric supply to said solenoid valve so as tooperate the solenoid valve upon obtainment of high pressure and lowpressure limit positions of the said switch, said pressure switchincluding means for adjusting the limit positions thereof.

7. In combination, an elastic air-tight walled membrane; means forsupplying air under pressure back of said membrane; means physicallyremoved from said membrane and responsive to the pressure of the air;and valve means under the control of the pressure responsive means forperiodically interrupting said air flow and interconnecting saidmembrane to the atmosphere for discharge upon a predetermined maximumlimiting pressure being reached.insaid.pressure-responsive means andre-.

mined minimum. pressure.

8. The method of assuring a free flow of material from a storage binhaving therein a flexible membrane secured to a back plate, across whichflexible membrane said material passes, comprising distending saidmembrane with air from an external source to build up the pressureagainst said membrane to a predetermined maximum; momentarilydiscontinuing, from a removed control point, the supply of air to saidmembrane releasing the air against said membrane and exhausting the sameinto the atmosphere to permit the membrane to collapse; and upon apredetermined minimum pressure against said membrane being reachedcontinuing from said removed control point the supply of air against themembrane, whereby intermittent discharge of said membrane is had at arate depending upon the maximum and minimum pressures against the same.j

9. In combination, a bin or hopper having sloping walls for the storageor discharge of material therefrom; an elastic, air-tight walledmembrane provided on the inner surface of said bin in the path of saidmaterial; means for supplying air under pressure back of said membrane;andmeans, physically removed from said memhrane and in circuit with saidair-supply means, for controlling the flow of air to said membrane inresponse to predetermined maximum and predetermined minimum pressurevalues of the air circuit including valve means under the control ofsaid pressure responsive means for periodically interrupting said airflow and interconnecting the said membrane to the atmosphere fordischarge upon the maximum pressure being reached and restablishing saidair flow upon reaching said minimum pressure.

References Cited in the file of this patent UNITED STATES PATENTS1,570,795 Tainton Jan. 26, 1926 1,927,583. Ernst Sept. 19, 19332,170,258 Borch Aug. 22, 1939 2,273,679 Westberg Feb. 17, 1942 2,353,346I Logan July 11, 1944 2,376,348 Fox May 22, 1945 2,381,802 Booth et alAug. 7, 1945 2,646,905 Vincent July 28, 1953

